1. Field of the Invention
This invention relates to improvements in a one-way clutch bearing.
2. Description of the Prior Art
Two types of one-way clutch bearing, i.e., the sprag type and the roller type, are known.
The sprag type one-way clutch bearing is comprised of an outer race having an annular inner surface, an inner race having an outer surface corresponding to and concentric with the inner surface, and a plurality of sprags disposed in an annular space formed between the inner and outer surfaces. When the inner race rotates in one direction, the upper and lower cam surfaces of the sprags become inclined to a position in which they do not transmit a torque, and permit relative rotation of the inner race and the outer race. On the other hand, when the inner race is about to rotate in the other direction, the cam surfaces of the sprags move and the sprags are inverted to prevent relative rotation of the inner and outer races, whereby a torque is transmitted from the inner race to the outer race.
On the other hand, the roller type one-way clutch bearing has a construction in which rollers are contained in roller containing grooves formed in one of an inner race and an outer race and are biased by springs in such a direction that the clearance between the bottom surface and the circumferential surface of the grooves becomes narrow. When one of the inner race and the outer race is driven in a certain direction, it rotates idly, and when one of the inner race and the outer race is driven in the other direction, the rollers roll in the roller containing grooves and bite between the bottom surface and the circumferential surface of the grooves to prevent relative rotation of the inner race and the outer race, whereby a torque is transmitted.
The above-described conventional one-way clutch bearings maintain a long life as long as they are used under a load torque of a predetermined value or less, but if an accidental excessive torque is imparted thereto, the sprags or the rollers may go beyond a predetermined torque transmitting position and further push into the inner and outer races, thereby leaving impressions on the surface of the sprags or the rollers which is in contact with the inner and outer races, or breaking the sprags or the rollers. Also, in such a case, the rollers may jump out toward the non-torque-transmitting side, i.e., the side of the springs which bias the rollers, thereby damaging the springs.
To eliminate such inconveniences, one might provide, in the case of the sprag type, a planar portion at a location beyond the cam surface which transmits a predetermined torque, and in the case of the roller type, to hold the rollers at an allowed maximum torque transmitting position by holding means, thereby causing the sprags or the rollers to slide when an excessive torque is imparted. However, when an excessive torque is imparted to a one-way clutch bearing actually using the above-described sprags or rollers, the slight movement of the posture of the sprags or rollers when they have begun to slide appears in the form of a variation in transmission torque and the sprags or rollers jump and cannot slide stably.